The basic objectives of this project are: 1) To investigate the activity of Cyclophosphamide and 5-Fluorouracil in advanced prostatic cancer, 2) To determine if sequential therapy with these agents is clinically useful, 3) To demonstrate their therapeutic effectiveness against current standard therapy, 4) To determine the predictive value of the in vitro evaluation of chemotherapeutic agents using such indicators as 5-Alpha-Reductase, Arginase and DNA Synthesis. Our institution is one of five major medical institutions collaborating in a similar project. Eligible patients with metastatic prostatic carcinoma will be randomized into one of three treatment groups: 1) Fluorouracil weekly intravenously every three weeks at a dose of 600 mgm/M2; 2) Cyclophosphamide intravenously every three weeks at a dose of 1 gram/m2; or 3) standard therapy. Patients will be treated for a minimum of twelve weeks at which time if progression occurs while under treatment with either of the two study drugs a cross over to the alternate agent will be done. Should progression occur after cross over, patients may be treated at the discretion of the investigators, but will be followed to death. Patients randomized to the standard treatment arm will also be followed to death. Indicators for prostatic cancer activity will be monitored prior to randomization and throughout the period of study.